Pneumatically tuned vehicle powertrain mounts

ABSTRACT

A system for securing a powertrain component to a body structure of a vehicle may include first and second mounts each having a base and a first elastomeric barrier secured to and extending from the base defining an air filled chamber, and a connector coupling the air filled chambers, the connector sized to provide an associated air volume that reduces stiffness of the first elastomeric barrier at an excitation frequency corresponding to a target engine speed. The air filled chambers may be hermetically sealed and pressurized above atmospheric pressure. The system may include a fluid-filled switchable mount having a decoupler air pocket selectively coupled to a vacuum source or atmosphere with an expander integrated with the mount or as a separate component coupled between the decoupler air pocket and the vacuum source. The expander may be implemented as a Helmholtz resonator or may include an in-line expansion chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/598,426filed Jan. 16, 2015 now U.S. Pat. No. 10,001,191 issued Jun. 19, 2018,the disclosure of which is hereby incorporated in its entirety byreference herein.

TECHNICAL FIELD

This disclosure relates to pneumatically tuned passive andactive/switchable mounts for connecting vehicle powertrain components toa vehicle underbody structure or chassis.

BACKGROUND

Various types of mounts have been used to secure vehicle powertraincomponents, such as an engine, electric motor, transmission, etc. to theunderbody structure of the vehicle. Mounts may include rubber or similarelastomeric materials to dampen or isolate various types of motionassociated with the vehicle powertrain to reduce transmission to therest of the vehicle, particularly the vehicle cabin where it may beperceived by vehicle occupants as noise or vibration. Mounts may includevarious materials or features that provide a desired frequency responseand may be selectively tuned by design or actively controlled duringvehicle operation to provide more attenuation or damping at frequenciesassociated with certain powertrain component operating modes, such asengine idling or lugging, for example. Other damping or stiffnesscharacteristics may be used to provide desired performance for operatingmodes having different characteristic frequencies that may be associatedwith road surface conditions, engine or motor speed changes, etc.

Hydraulic, hydroelastic, or hydro-mounts are commonly used in passengercar applications and include a chamber filled with glycol or hydraulicfluid to isolate idle and part/open throttle powertrain excitations, aswell as for controlling vehicle shake under road inputs. Depending onthe particular application and implementation, designs may includepassive hydro-mounts or actively controlled/switchable hydro-mounts.Switchable hydro-mounts may include an idle mode of operation thatprovides a reduction in stiffness at the frequency range of enginefiring order excitations at engine idle speeds, and a shake mode thatprovides increased damping for large excitations while concurrentlyproviding low dynamic stiffness for small amplitude excitations athigher frequencies (such as 20 Hz and above) through a decoupler.Switching between a default mode (ride or cruise mode, for example) andidle mode is typically achieved by applying vacuum to the rubbermembranes including the decoupler of the hydro-mount using an associatedcontrol valve. However, various designs may provide unfavorablestiffness during operating modes when vacuum is not applied,particularly within frequency ranges associated with operating modessuch as engine lugging, for example.

SUMMARY

Various embodiments according to the present disclosure may include asystem for securing a powertrain component to a body structure of avehicle having first and second mounts each having a base and a firstelastomeric barrier secured to and extending from the base defining anair filled chamber, and a connector coupling the air filled chambers,the connector sized to provide an associated air volume that reducesstiffness of the first elastomeric barrier at an excitation frequencycorresponding to a target engine speed, such as an excitation frequencyexceeding 20 Hertz associated with engine lugging conditions. Theconnector and air filled chambers may be hermetically sealed and may bepressurized above atmospheric pressure. The first and second mounts mayeach include a second elastomeric barrier secured to and extending fromthe base and enveloping the first elastomeric barrier, the secondelastomeric barrier defining a fluid chamber having a fluid with aspecific gravity greater than unity, such as hydraulic fluid or glycol,for example. Each base may include a channel connecting the fluidchamber to an associated fluid bellows chamber. The system may alsoinclude a switch selectively coupling the connector and air filledchambers to a vacuum source.

Embodiments may also include a method for mounting a powertraincomponent in a vehicle that includes pneumatically coupling air pocketsof left and right powertrain mounts disposed between the powertraincomponent and a vehicle chassis using a connector having a size andlength selected to reduce stiffness of the left and right mounts withinat least one predetermined excitation frequency range. The method mayinclude hermetically sealing the air pockets and the connector andpressurizing the air pockets to a pressure above atmospheric pressure.In various embodiments, the left and right powertrain mounts eachinclude an elastomeric decoupler cooperating with a channel plate toform the air pockets, and an elastomeric cover cooperating with thechannel plate to form a fluid filled chamber surrounding the elastomericdecoupler.

In some embodiments, a vehicle powertrain mounting system includes achannel plate defining air and fluid channels, an elastomeric decouplercooperating with the channel plate and forming an air pocket coupled tothe air channel and a vacuum source via a connector and valve, anelastomeric cover forming a fluid chamber that surrounds the decouplerand couples with a bellows chamber via the fluid channel, and anexpander defining an air expansion chamber coupled to the air channel.The expander may have a volume of at least ten times a volume of the airpocket of the elastomeric decoupler to filter out air dynamics in theconnector. The expander may include a first port coupled to the airpocket and a second port coupled to the connector. The expander may beintegrated within a cap secured to the channel plate or disposed betweenthe connector and the valve associated with the vacuum source. The valvemay be operated based on vehicle operating parameters, such as enginespeed and vehicle speed to alternatively couple the connector to thevacuum source or to atmosphere.

In some embodiments, a vehicle powertrain mounting system includes achannel plate defining air and fluid channels, an elastomeric decouplercooperating with the channel plate and forming an air pocket coupled tothe air channel and a vacuum source via a connector and valve, anelastomeric cover forming a fluid chamber that surrounds the decouplerand couples with a bellows chamber via the fluid channel, and aHelmholtz resonator having a volume coupled to the connector by a singleinput/output port. The Helmholtz resonator may be tuned based on an aircolumn within the connector to reduce stiffness within a predetermineddecoupler excitation frequency range, such as a frequency rangeassociated with engine lugging conditions, for example.

Various embodiments according to the present disclosure may provide oneor more advantages. For example, modifying or tuning of the naturalfrequency or frequency response of the air column associated with ahydro-mount decoupler may improve isolation in higher frequency ranges,such as 20 Hz and above. Insertion of an expansion chamber havingseveral times the displaced volume of the decoupler may act as amechanical filter for the air column frequencies to modify the frequencyresponse. Similarly, use of a Helmholtz resonator tuned to a selectedair column mode in the within a target frequency range may be used tomodify the frequency response and improve isolation for a desiredfrequency range.

Embodiments according to the present disclosure having pneumaticallycoupled mounts have the ability to tune the air column mode(s) for dipsin stiffness where lower stiffness is desired. Tuning of the air columnmay be accomplished with the area and length of the connector as well asthe air pressure within the connector for embodiments havinghermetically sealed couplings. In various embodiments, air tuningprovides increased damping or dips at engine lugging frequencies whileconcurrently providing hydraulic damping for large amplitude shakereducing or eliminating the need for a lugging track. Coupling of leftand right mounts may be used to increase stiffness where left and rightmotion is in-phase, such as produced by engine bounce. Variousembodiments may incorporate tuned coupling of left and right mounts intoexisting switchable hydraulic mounts to provide active switching incombination with passive switching associated with in-phase motion ofthe left and right mounts.

The above advantages and other advantages and features will be readilyapparent from the following detailed description of the embodiments whentaken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a system or method for securing apowertrain component such as an engine, motor, and/or transmission to avehicle structure having left and right hydraulic mounts withpneumatically connected decouplers according to various embodiments ofthe disclosure;

FIG. 2 is a graph illustrating stiffness reduction associated with airtuning and coupling of left and right powertrain mounts according tovarious embodiments of the disclosure;

FIG. 3 is a block diagram illustrating a system for securing apowertrain component to a vehicle having passive left and right mountswith a hermetically sealed connector sized to tune the air column forreduced stiffness for targeted vehicle operating conditions according tovarious embodiments of the disclosure;

FIG. 4 is a block diagram illustrating a powertrain component mountingsystem or method having an expansion chamber or Helmholtz resonatorpositioned in-line between the decoupler and a vacuum source accordingto various embodiments of the disclosure;

FIG. 5 illustrates the effect of powertrain mount stiffness tuning orreduction associated with an expansion chamber between the decoupler andvacuum source according to various embodiments of the disclosure;

FIGS. 6 and 7 illustrate passive-side velocity improvements as afunction of engine speed associated with a right-side and left-sidemounts, respectively, having an expansion chamber according to variousembodiments of the disclosure;

FIG. 8 is a block diagram illustrating a mount having an integratedexpansion chamber associated with the air pocket of the decoupleraccording to various embodiments of the disclosure; and

FIG. 9 is a graph illustrating comparisons of component-level stiffnessphase and amplitude measurements for left-hand and right-hand mountswith vacuum lines, without vacuum lines, and with vacuum lines andexpansions chambers according to various embodiments of the presentdisclosure.

DETAILED DESCRIPTION

As required, detailed embodiments are disclosed herein; however, it isto be understood that the disclosed embodiments are merely exemplary andmay be embodied in various and alternative forms. The figures are notnecessarily to scale; some features may be exaggerated, minimized, oromitted to show details of particular components. Therefore, specificstructural and functional details disclosed herein are not to beinterpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention. Various representative embodiments include components orfeatures having similar construction and function as will be apparent tothose of ordinary skill in the art. As such, features or components thatare not described as being positioned or operating differently fromthose similar features or components described with respect to anotherembodiment are assumed to operate in a similar manner or perform asimilar function although not explicitly labeled or described.Similarly, those of ordinary skill in the art will recognize that theblock diagrams may omit certain details with respect to the hardware forsecuring the mount to a powertrain component, or to a vehicle chassis orother underbody structure.

FIG. 1 is a block diagram illustrating a system or method for securing apowertrain component such as an engine, motor, and/or transmission to avehicle structure having left and right hydraulic mounts withpneumatically connected decouplers according to various embodiments ofthe disclosure. System 100 includes a first mount 102 and a second mount104 each having a base 106, 108, respectively, and a first elastomericbarrier 110, 112 secured to and extending from the base 106, 108defining an air filled chamber 114, 116. A connector 118 couples the airfilled chambers 114, 116 via corresponding air channels 120, 122 throughbases or channel plates 106, 108. Connector 118 is sized to provide anassociated air volume that reduces stiffness of the first elastomericbarriers 110, 112 at an excitation frequency corresponding to a targetengine speed or excitation frequency, such as an engine lugging range,for example. Elastomeric barriers 110, 112 in combination withassociated air pockets 114, 116 are often referred to as decouplers. Invarious embodiments, connector 118 is sized to provide an associated airvolume that reduces stiffness of the first elastomeric barrier 110, 112at an excitation frequency exceeding 20 Hertz.

In some embodiments, connector 118 and air-filled chambers or pockets114, 116 may be hermetically sealed. Some embodiments may include apressurized coupling with the air within connector 118 and decoupler airpockets 114, 116 having a pressure above ambient or atmosphericpressure. As the atmospheric (or barometric) pressure changes based onaltitude and environmental conditions, the pressurized coupling may bepressurized based on a differential above current barometric pressure.Alternatively, the system pressure may be selected based on designconsiderations to best manage noise, vibration, and harshness (NVH) fora majority of anticipated operating conditions and fixed during vehicleassembly. Tuning of the air column coupling the complementary mounts canbe accomplished using not only the area and length of connector 118, butthe stiffness reduction or dip can be enhanced by increasing thepressure of the air within the column.

As illustrated and described with respect to the embodiments of FIGS. 4,8, and 9, for example, the embodiments of FIGS. 1 and 3 may also includea controllable solenoid valve to selectively connect connector 118 to avacuum source, atmosphere, or a pressure source. In contrast to thoseembodiments where such a valve is used to alternatively couple theconnector 118 and the associated air column to a vacuum source or ventto atmosphere, embodiments having two mounts 102, 104 coupled by aconnector 118 may selectively control an associated valve to coupleconnector 118 and the associated air column to the vacuum source, toatmosphere, or to seal the pneumatic system. For applications andimplementations employing a pressurized pneumatic coupling betweencomplementary mounts 102, 104, a corresponding solenoid valve may becontrolled to selectively couple connector to an air pump or compressorto increase air pressure above atmospheric or ambient barometricpressure. As generally understood by those of ordinary skill in the art,a controllable solenoid valve may be used to dynamically vary or modifythe frequency response or stiffness amplitude and phase of the mountbased on current powertrain and vehicle operating conditions to bettermanage NVH under varying road surface inputs, as well as vehicle andambient operating conditions.

As also illustrated in the block diagram of FIG. 1, a second elastomericbarrier 124, 126 is secured to and extends from the base 106, 108 andenvelops or surrounds the first elastomeric barrier 110, 112 andassociated air pocket 114, 116. The second elastomeric barrier 124, 126defines a fluid chamber 128, 130 having a fluid with a specific gravitygreater than unity, such as hydraulic fluid or glycol, for example. Eachbase 106, 108 (or channel plate) includes a fluid channel 132, 134connecting the fluid chamber 128, 130 to an associated fluid bellowschamber 136, 138.

As generally illustrated in FIG. 1, the pneumatically coupled hydraulicmounts may respond differently to various inputs depending on whetherthe inputs are in-phase or out-of-phase with respect to the mountlocations. In one embodiment, a powertrain is secured to the underlyingvehicle structure using two (2) mounts with one mount positioned on theleft-hand (LH) side of the engine and the other mount positioned on theright-hand (RH) side of the engine. Smaller amplitude vibrationsgenerally categorized as contributing to NVH are indicated by arrows140, 142 and excite the mounts out-of-phase. As such, one mount pushes(pressurizes) the air column while the other mount pulls (createsvacuum) in the air column providing harmonic excitation from both ends.In contrast, larger amplitude inputs, such as powertrain bounce produceinputs generally indicated by arrows 150, 152, which are in-phase or ingenerally the same direction at the same time. Coupling of thecomplementary LH and RH mounts facilitates air column tuning to providereduced stiffness at lugging frequencies to better manage NVH while atthe same time providing hydraulic damping for large amplitude shake,which may alleviate the need for a lugging track if the dip or stiffnessreduction is sufficient. Alternatively, this arrangement can be used toenhance a lugging track, but would not benefit from the hydraulicdamping at shake in these implementations. An arrangement such asillustrated in FIG. 1 provides passive switching for powertrain shake.Engine shake is usually dominated by engine bounce. Strategic tuning ofthe pneumatic coupling will increase the stiffness for shake where theLH and RH motion are in-phase as represented by arrows 150, 152, whichincreases the air pressure associated with the decoupler air pockets114, 116 and connector 118.

FIG. 2 is a graph illustrating stiffness reduction associated with airtuning and coupling of left and right powertrain mounts according tovarious embodiments of the disclosure. Stiffness (N/mm) is plotted as afunction of excitation frequency (Hz). Line 210 represents the stiffnessresponse with conventional hydraulic tuning. Line 212 represents thestiffness response with the addition of air column tuning according toembodiments of the present disclosure. As illustrated, the stiffnesspeaks at 208 around 900 N/mm around 15 Hz. The conventional hydraulicmounts have a relatively flat response above about 20 Hz. In contrast,the addition of air tuning according to various embodiments providesreduced stiffness or a stiffness dip, generally indicated at 214, whichbegins above 20 Hz at 216 and extends to about 70 Hz at 218.

FIG. 3 is a block diagram illustrating a system for securing apowertrain component to a vehicle having passive left and right mountswith a hermetically sealed connector sized to tune the air column forreduced stiffness associated with targeted vehicle operating conditionsaccording to various embodiments of the disclosure. System 300 includeshermetically sealed and pneumatically coupled complementary mounts 302,304 each having a base or sealing plate 306, 308. An elastomeric barrieror cover 324, 326 cooperates with an associated sealing channel plate306, 308, to define corresponding air-filled chambers 328, 330. Airchannels 320, 322 extend through sealing channel plates 306, 308 tocouple air-filled chambers 328, 330 to one another via connector 318.The embodiment of the powertrain mounts illustrated in FIG. 3 does notinclude decouplers and does not rely on fluid other than air (such ashydraulic fluid or glycol) to provide dynamic stiffness. Rather, the aircolumn connecting chambers 328, 330 may be tuned by appropriateselection of the size and length of connector 318 as previouslydescribed. As with other embodiments described with respect to FIG. 1,the pneumatically coupled hermetically sealed system of FIG. 3 may alsoinclude a vacuum source and associated control valve, or may havepressurized air at a pressure exceeding atmospheric or ambient pressure.Embodiments as generally illustrated in FIG. 3 provide similaradvantages with respect to providing reduced stiffness for targetoperating conditions, such as engine lugging conditions, for example.

FIG. 4 is a block diagram illustrating a powertrain component mountingsystem or method having an expansion chamber positioned between thedecoupler and a vacuum source according to various embodiments of thedisclosure. Vehicle powertrain mounting system 400 includes a channelplate 406 defining an air channel 420 and a fluid channel 432. Anelastomeric decoupler 410 cooperating with channel plate 406 forms anair pocket 414 coupled to air channel 420 and a vacuum source 462 via aconnector 418 and a valve 460. An elastomeric cover 424 cooperates withchannel plate 406 forming a fluid chamber 428 that surrounds decoupler410 and couples with a bellows chamber 436 via fluid channel 432. Anexpander 458 defines an air expansion chamber 470 coupled to air channel420. Expander 458 may have a volume sufficient to generate a stiffnessresponse substantially similar to when no vacuum is applied to decoupler410. In one embodiment, expander 458 has a volume of at least ten timesgreater than a volume of the air pocket 414 of the elastomeric decoupler410. As illustrated in FIG. 4, expander 458 is positioned in-line withair channel 420 and connector 418 with a first port 454 coupled to airpocket 410 and a second port 456 coupled to connector 418. Expansionchamber 470 acts as a mechanical filter for excitation from decoupler410 as well as for feedback from vacuum tube or connector 418 into thedecoupler air pocket 414. Addition of expansion chamber 470 prevents theair column resonant mode from being excited when operating in ride modewith valve 460 venting to atmosphere 464.

As also shown in FIG. 4, various embodiments may employ a Helmholtzresonator 458′ having a chamber or reservoir 470′ eliminating expander458. As compared to expander 458, Helmholtz resonator 458′ includes asingle inlet/outlet port 472 that couples the volume or space of chamber470′ to connector 418. One or more Helmholtz resonators may be coupledto the air column to act as tuned dampers on acoustic modes of the aircolumn. The Helmholtz air column mode may be tuned to the vacuum line418 air column mode(s), which has the effect of dividing the air columnmodal excitation into two smaller resonances that occur at a higher andlower frequency that the resonance without the Helmholtz resonator.Helmholtz resonator 470′ may be tuned based on the air column mode(s)within the connector 418 to reduce stiffness within a predetermineddecoupler excitation frequency range. In various embodiments, thepredetermined decoupler excitation frequency range corresponds to enginelugging conditions.

FIG. 5 illustrates the effect of powertrain mount stiffness tuning orreduction associated with an expansion chamber between the decoupler andvacuum source according to various embodiments of the disclosure. Thegraph of FIG. 5 plots steering wheel vibration (mm/s) as a function ofengine speed (RPM) to illustrate engine lugging response. Datarepresented by line 508 corresponds to active or switchable mounts withvacuum lines removed. Data represented by line 510 corresponds to activeor switchable mounts with vacuum lines and associated air columns. Datarepresented by line 512 corresponds to mounts having an expander with anexpansion chamber as illustrated and described with reference to FIG. 4,for example. As illustrated by lines 508 and 512, adding an expansionchamber in-line with the vacuum line or connector provides asubstantially similar response as that provided when the vacuum linesare removed.

FIGS. 6 and 7 illustrate passive-side velocity improvements associatedwith an expansion chamber as a function of engine speed for right-sideand left-side mounts, respectively. FIGS. 6 and 7 plot passive-sidevelocity as a function of engine speed to illustrate vehicle-levelmeasurements for an engine lugging response. Data represented by lines610, 710 correspond to conventional mounts without an expansion chamber.Data represented by lines 612, 712 correspond to mounts having anexpansion chamber according to various embodiments. As illustrated inthe plots of FIGS. 6 and 7, addition of an expansion chamber between thedecoupler and vacuum source provides significant reductions at themounts.

FIG. 8 is a block diagram illustrating a mount having an integratedexpansion chamber associated with the air pocket of the decoupleraccording to various embodiments of the disclosure. Vehicle powertrainmounting system 800 includes a channel plate 806 defining an air channel820 and a fluid channel 832. An elastomeric decoupler 810 cooperatingwith channel plate 806 forms an air pocket 814 coupled to air channel820 and a vacuum source 862 via a connector 818 and a valve 860. Anelastomeric cover 824 cooperates with channel plate 806 forming a fluidchamber 828 that surrounds decoupler 810 and couples with a bellowschamber 836 via fluid channel 832. An integrated expander 858 defines anintegrated air expansion chamber 870 coupled to air channel 820.Expander 858 may have a volume sufficient to generate a stiffnessresponse substantially similar to when no vacuum is applied to decoupler810. In one embodiment, expander 858 has a volume of at least ten timesgreater than a volume of the air pocket 814 of the elastomeric decoupler810. As illustrated in FIG. 8, expander 858 is positioned in-line withair channel 820 and connector 818 with a first port 854 coupled to airpocket 810 and a second port 856 coupled to connector 818. Expansionchamber 870 acts as a mechanical filter for excitation from decoupler810 as well as for feedback from vacuum tube or connector 818 into thedecoupler air pocket 814. Addition of expansion chamber 870 prevents theair column resonant mode from being excited when operating in ride modewith valve 860 venting to atmosphere 864.

FIG. 9 is a graph illustrating comparisons of component-level stiffnessphase and amplitude measurements for left-hand and right-hand mountswith vacuum lines, without vacuum lines, and with vacuum lines andexpansion chambers according to various embodiments of the presentdisclosure. All the configurations tested were operated in ride modewith no vacuum applied. FIG. 9 plots phase angle (degrees) and scaledstiffness (k*N/mm) as a function of excitation frequency (Hz). Datarepresented by lines 910, 912 correspond to RH and LH mounts,respectively, with vacuum lines. Data represented by lines 914, 916correspond to RH and LH mounts, respectively, with vacuum lines and anexpansion chamber having a volume of 30 cc. Data represented by line 918corresponds to RH/LH mounts without vacuum lines. The stiffness peaksgenerally indicated at 930 and 932 are associated with the dynamicinteraction of the air column modes in the vacuum lines in response todecoupler motion. The addition of 30 cc expansion chambers producessimilar stiffness values as mounts without vacuum lines effectivelyeliminating the stiffness peaks.

As generally illustrated in the embodiments of FIGS. 1-3, a method formounting a powertrain component in a vehicle may include pneumaticallycoupling air pockets of left and right powertrain mounts disposedbetween the powertrain component and a vehicle chassis using a connectorhaving a size and length selected to reduce stiffness of the left andright mounts within at least one predetermined excitation frequencyrange. The method may further include hermetically sealing the airpockets and the connector, and pressurizing the air pockets to apressure above atmospheric pressure.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments that may not be explicitlydescribed or illustrated. While various embodiments could have beendescribed as providing advantages or being preferred over otherembodiments or prior art implementations with respect to one or moredesired characteristics, those of ordinary skill in the art recognizethat one or more features or characteristics can be compromised toachieve desired overall system attributes, which depend on the specificapplication and implementation. These attributes may include, but arenot limited to cost, strength, durability, life cycle cost,marketability, appearance, packaging, size, serviceability, weight,manufacturability, ease of assembly, etc. As such, embodiments describedas less desirable than other embodiments or prior art implementationswith respect to one or more characteristics are not outside the scope ofthe disclosure and can be desirable for particular applications.

What is claimed is:
 1. A system for securing a powertrain component to abody structure of a vehicle, comprising: first and second mounts eachhaving a base and a first elastomeric barrier secured to and extendingfrom the base defining an air filled chamber, each base having a firstchannel extending therethrough and coupling the air filled chamber to aconnector port; and a connector configured to be secured to theconnector port of each base coupling the air filled chambers, theconnector also configured to, in cooperation with the first channelextending through each base, provide an associated air volume thatreduces stiffness of the first elastomeric barrier at an excitationfrequency corresponding to a specified engine speed.
 2. The system ofclaim 1 wherein the connector and air filled chambers are hermeticallysealed.
 3. The system of claim 2 wherein the connector and the airfilled chambers are pressurized above atmospheric pressure.
 4. Thesystem of claim 1, the first and second mounts each comprising: a secondelastomeric barrier secured to and extending from the base andenveloping the first elastomeric barrier, the second elastomeric barrierdefining a fluid chamber having a fluid with a specific gravity greaterthan unity.
 5. The system of claim 4 wherein each base includes a secondchannel connecting the fluid chamber to an associated fluid bellowschamber.
 6. The system of claim 4 wherein the connector is configured toprovide an associated air volume that reduces stiffness of the firstelastomeric barrier at an excitation frequency exceeding 20 Hertz. 7.The system of claim 4 further comprising: a switch selectively couplingthe connector and air filled chambers to a vacuum source.
 8. The systemof claim 1 wherein the connector comprises a diameter and lengthconfigured to provide, in cooperation with the first channel of thefirst and second mounts, an associated air volume to reduce stiffness ofthe first elastomeric barrier at an excitation frequency correspondingto an engine lugging speed.
 9. The system of claim 1 wherein theconnector comprises a Helmholtz resonator.
 10. The system of claim 1further comprising a Helmholtz resonator coupled to the connector. 11.The system of claim 1 wherein the connector comprises an air chamber.12. The system of claim 1 further comprising an expansion chamber havinga volume of at least ten times a volume of each air filled chamber. 13.A method for mounting a powertrain component in a vehicle, comprising:pneumatically coupling air pockets of left and right powertrain mountsdisposed between the powertrain component and a vehicle chassis, thepowertrain mounts each including a channel extending from an associatedair pocket to an associated coupling port, using a connector configuredto connect the coupling port of the powertrain mounts and, incooperation with the channel of the powertrain mounts, reduce stiffnessof the powertrain mounts within at least one predetermined excitationfrequency range.
 14. The method of claim 13 further comprising:hermetically sealing the air pockets and the connector; and pressurizingthe air pockets to a pressure above atmospheric pressure.
 15. The methodof claim 13 wherein the at least one predetermined excitation frequencyrange corresponds to engine speed associated with engine lugging. 16.The method of claim 13 further comprising coupling an expander to theconnector wherein the expander has a volume of at least ten times avolume of each of the air pockets.
 17. The method of claim 16 whereinthe expander comprises a Helmholtz resonator.